In a weaving mill it is necessary to have or produce for the looms warp beams where all the warp threads or yarns are of identical length from one beam to the next. It is also important that all the beams of a given production run have the same diameter, the result being that the filament density is the same on all the beams. Thus it is in general known to monitor the length wound on the beam and the number of revolutions the beam made to wind up this length for a first model wound warp, and then to use these values as set points comparable to actual values determined during the winding of subsequent beams.
In German 32 06 272 of Koslowski the number of beam revolutions and the length of wound filament is continuously monitored, with respective set-point outputs produced and recorded for the model wound warp, that is the first of a series of wound warps that are supposed to be identical. The actual values of the number of beam revolutions and the length being wound in subsequent cycles for copies are compared to the respective set points and correction are made by changing the warp-beam rotation rate, acting on thread brakes in a filament-supply creel, or braking a packing roll so bring the actual values back to the respective set points. The filament length is determined simply by passing the entire warp sheet over a measuring roller coupled to rotation-detecting and -measuring sensor.
Another such system shown in EP 1,219,738 of Hane the beam rotation and the warp length are monitored to determine how much warp is wound up with each revolution of the beam, and this value is stored. The same values for copies are compared with the stored values to generate a difference signal. The tension in the warp is varied to keep the actual-value signals identical or close to the set-point signals, that is to reduce the respective difference signals to the smallest possible levels. When the warp filaments are elastic so that they can stretch, this is a problem. The actual-value of the filament length being wound is determined by passing the incoming warp sheet over a measuring roller, or by pressing a measuring roller against the wound warp on the warp beam.
There are substantial problems with these systems at the start and end of each winding cycle, that is the winding of a single copy beam. Excessive braking of a rotating beam can produce so much slack as to make the wound warp unusable, and excessive acceleration can tension the filaments enough to break or stretch them.
Accordingly, German 36 04 790 of Guillot describes a system where the density of the copies is controlled by varying the radial pressure exerted on the warp being wound by a packing roller. The actual value for the filament length is determined by a separate measuring roller also radially engaging the warp being wound. With this system the diameter of the warp being wound is used to determine the filament length for a given rotation of the beam, producing a partial length that is stored and compared with that of subsequent copies, with the packing roller pressure varied to produce uniformity. Such a system therefore has both a packing roller and a length-measuring roller.
In U.S. Pat. No. 5,257,462 of Butterman the warping system has a packing roller bearing upon the warp being wound and mechanically connected with a displacement detecting transducer that emits measurement impulses, a beam-driven shaft encoder that emits a predetermined number of calculation impulses for each revolution of the beam, and a computer that calculates the partial lengths of the warp layers or laps from the measurement impulses and the calculation impulses. The displacement-detecting transducer is movably or slidingly interengaged with an elongated linear member in the form of a toothed rack hinged so that a projection of one end always intersects the longitudinal axis of the lap beam. A correction read-out is calculated from the diameter of the axle of the lap beam and the position of the point of interengagement of the elongated linear member with the displacement detecting transducer through the pressure point of the packing roller bearing upon material wound upon the lap beam and the number of rotations of the lap beam. Such a system can calculate the total filament length and the wound density, but is quite complex.